1. Field of the Invention
The present invention relates to a metal clad door whose structure and materials are selected in view of improving its acoustic insulation properties.
2. Brief Description of the Prior Art
A plurality of metal clad, acoustic doors are presently known and/or available on the market, of which one is described and claimed in Canadian patent No. 858.917 (SHERMAN) issued on Dec. 22, 1970.
The door of the above-mentioned patent comprises a principal panel as well as a floating panel connected together through a rubber extrusion. However, the latter extrusion does not fully insulate the principal and floating panels from each other. Indeed, a mechanical interconnection exists between the exterior sheet metal covering of the two panels at the bottom of the door, which interconnection establishes an acoustic short circuit. This acoustic short circuit enables direct transmission of sound waves from one side of the door to the other side thereof.
Moreover, a fiberglass insulation is confined within the interior of the door and consequently does not contribute in acoustically insulating the door. More specifically, the fibers cannot move, and accordingly do not vibrate to transform the mechanical energy of the acoustic waves into heat to thereby eliminate the same.
The space of air within the door of the above-mentioned Canadian patent is also too small. This creates a frequency mass-air-mass causing an effect of spring into resonance between the two panels at low frequency within the frequency range of interest, namely 125-4000 Hz. Acoustic waves at this resonance frequency can accordingly be transmitted through the space of air from one mass to the other to cause a lack of sound insulation at this frequency.
Moreover, the above-mentioned rubber extrusion is apparent from the outside of the door. Therefore, the metal clad door of Canadian patent No. 858.917 is not fire resistant as the rubber of the extrusion is combustible and exposed to the fire on the outside of the door.